Bump mpath and mongoose

Bumps [mpath](https://github.com/aheckmann/mpath) to 0.8.4 and updates ancestor dependency [mongoose](https://github.com/Automattic/mongoose). These dependencies need to be updated together.


Updates `mpath` from 0.8.3 to 0.8.4
- [Changelog](https://github.com/mongoosejs/mpath/blob/master/History.md)
- [Commits](mongoosejs/mpath@0.8.3...0.8.4)

Updates `mongoose` from 5.13.7 to 5.13.21
- [Release notes](https://github.com/Automattic/mongoose/releases)
- [Changelog](https://github.com/Automattic/mongoose/blob/5.13.21/History.md)
- [Commits](Automattic/mongoose@5.13.7...5.13.21)

---
updated-dependencies:
- dependency-name: mpath
  dependency-type: indirect
- dependency-name: mongoose
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]